Heretofore, as an interior panel to be used for transport machinery such as rolling stock, automobiles, aircraft, or ships, and for building structures and the like, there has been proposed a light weight type highly rigid panel having protrusions and recesses provided in a zigzag pattern (for example, refer to Patent Document 1). This panel disclosed in Patent Document 1 is such that protrusions and recesses are formed side by side in two directions, namely the vertical direction and horizontal direction of a flat plate panel, and it is formed in a shape such that flat sections other than the protrusions and recesses are not formed linearly. Moreover, for a heat insulator to be used for heat insulation in a catalytic converter or a muffler of an automobile, there has been proposed a configuration in which protrusions are arranged side by side in two directions within a panel surface (for example, refer to Patent Document 2). In these panels, there are formed protrusions and recesses or just protrusions, arranged side by side in two directions within the panel surface, and thereby a higher level of rigidity is achieved for the same plate thickness compared to a flat plate with no protrusions or recesses formed thereon, or to a corrugated plate with protrusions and recesses formed only in one direction thereon.